The invention relates to an arrangement for attaching an electrical component to a mounting base and for connecting it galvanically to a terminal block connected to the mounting base. The arrangement of the invention is particularly suitable for use with components carrying higher currents, for example inductive components such as measuring transformers.
If the mounting base is a printed board, various soldering techniques are typically employed for attaching electrical components mechanically to the mounting base and for connecting them electrically to the terminal block connected to the mounting base. However, such techniques cannot be employed with higher currents, since the cross-sectional area of copper foil strips on conventional printed boards is not sufficient for conducting such currents. A typical example of a component carrying higher currents is a measuring transformer. In the following, known solutions will be dealt with particularly in the case of measuring transformers.
Transformers implemented as laminated core transformers are typically attached to the mounting base by iron binders which are secured to the base either by screws or other mechanical fasteners, such as rivets, or by bending the ends of the iron binders so that they attach the transformer mechanically to the base. The terminals for the primary and secondary winding in the transformers are provided by unfixed conductors. This conventional securing technique involves the laborious step of securing the iron binders. Providing the terminals in the transformers by unfixed conductors, in turn, entails the possibility of faulty coupling; in addition, it is very difficult to check the coupling visually, particularly if the there are several measuring transformers on the base, which is often the case.
In the same way as a laminated core transformer, it is possible to attach a toroidal transformer mechanically to the base either from its case or by a fastening means screwed through its centre. Even in this case, the terminals for the primary and secondary winding are provided by unfixed conductors. A toroidal transformer is thus not different from a laminated core transformer as regards the problems associated with the securing and coupling.
One alternative is to attach the transformer to a printed board from solder-tags and to provide the wiring by means of copper foil strips on the printed board. This printed board solution is, however, often uneconomic, since the copper foil strips must be made thicker than usual in order to provide conductors with a sufficient cross-sectional area. Moreover, the requirements set by the norms for the current-carrying capacity are not met if soft soldering is used.
Transformers which are moulded in plastic and in which terminals are soldered to the ends of the primary windings are also used to some extent in the field. However, moulding transformers in plastic requires large series, and because of the many different combinations, the production control and storage incur extra costs. The more there are transformers, the more difficult it is to mount them on a base and to provide a compact construction.
It should also be noted that in the case of measuring transformers it is necessary to apply the norm DIN 57435, concerning static measuring and protection relays. According to this norm, the requirement for continuous current-carrying capacity is a quadruple nominal current, the requirement for continuous thermal current-carrying capacity for one second is a hundredfold nominal current, and the requirement for dynamic current-carrying capacity is 2,5-fold thermal current-carrying capacity for one half-cycle. If the nominal current is, for example, 5 A, the requirement for continuous thermal current-carrying capacity grows to 500 A for 1 s, and the requirement for dynamic current-carrying capacity grows to 1250 A.